1. Field of the Invention
The present invention relates generally to an inductor and a method for manufacturing the inductor. More particularly, the present invention relates to an inductor for radio frequency (RF) devices for a system-on-a-chip (SOC), and a method of manufacturing the inductor.
2. Description of the Related Art
A SOC comprises a single microchip integrating together all of the elements of a system. The elements of the system generally comprise independently operating semiconductor devices or circuits. For example, a SOC for wireless communications typically includes a microprocessor, a digital signal processor (DSP), a random access memory (RAM) device, and a read only memory (ROM). Generally, the elements of a SOC are integrated on a large scale integrated (LSI) circuit or an integrated circuit (IC).
In a SOC for RF communication, semiconductor devices and RF circuits are generally integrated on a single chip. Inductors are typically formed on integrated circuits of the SOC after the integrated circuits are formed on a semiconductor substrate. A thin film type inductor having a spiral or solenoid construction is commonly employed in a SOC because it is easily combined with integrated circuits. In addition, thin film type inductors are employed for various devices such as a voltage controlled oscillator (VCO), a filter, or a converter.
A conventional thin film type inductor is disclosed in various international patent publications, including, for example, Korean Laid Open Patent Publication No. 2003-20,603, Korean Patent No. 348,250, and Japanese Laid Open Patent Publication No. 1998-241,983.
FIGS. 1A to 1C are cross-sectional views illustrating a method of manufacturing a conventional inductor disclosed in the above-mentioned Korean Laid Open Patent Publication.
Referring to FIG. 1A, a soft magnetic thin film 15 is formed on a substrate 10 formed on a silicon wafer. Soft magnetic thin film 15 has a double-layer structure comprising an iron-tantalum nitride (FeTaN) layer and a titanium (Ti) layer.
An insulation film 20 of silicon oxide is formed on soft magnetic thin film 15 and a seed layer 25 for an electroplating process is formed on insulation film 20. Seed layer 25 has a double-layer structure comprising a copper (Cu) layer and a chromium (Cr) layer.
A photosensitive film 30 is deposited on seed layer 25, and then a mask 35 is formed over photosensitive film 30. Photosensitive film 30 is exposed through a pattern in mask 35. The pattern of mask 35 defines an inductor having a coil structure.
Referring to FIG. 1B, a plurality of holes are formed through photosensitive film 30 by developing the exposed portions of photosensitive film 30. The holes expose seed layer 25 which is positioned beneath photosensitive film 30. A coil 40 of the inductor is formed from seed layer 25 to fill the holes. Coil 40 is formed by an electroplating process using a plating solution including copper.
Referring to FIG. 1C, photosensitive film 30 is removed and portions of seed layer 25 exposed between the loops of coil 40 are etched away using a wet etching process to complete coil 40 on insulation film 20. Coil 40 is attached to an upper magnetic film 50 using an adhesive film 45 of epoxy resin to form the inductor on substrate 10.
In the above-described method for manufacturing a conventional inductor, the rate at which coil 40 grows from seed layer 25 to fill the holes in photosensitive film 30 decreases significantly as the size of the holes increases. As the width and height of the inductor increase, the rate of coil growth slows accordingly, thus driving up the time and cost of manufacturing for the inductor and the related RF device. However, it is important for the inductor to have sufficient width and height to ensure the desired electrical characteristics of the inductor.